Control valve for a hydraulic control system



Oct. 5, 1965 G. PUSCH ETAL CONTROL VALVE FOR A HYDRAULIC CONTROL SYSTEM Filed May 14, 1962 United States Patent 3,209,783 CONTROL VALVE FOR A HYDRAULIC QQNTRUL SYSTEM Gerhard Pusch, Neuss-Reuschenberg, and Franz Henninghaus, Dusseldorf, Germany, assignors to International Harvester Company, Chicago, 111., a corporation of New Jersey Filed May 14, 1962, Ser. No. 195,668 Claims priority, application Germany, May 13, 1961, I 19,914 4 Claims. (Cl. 137625.67)

This invention relates to a control valve for a hydraulic control system adaptable for but not limited to use with position and draft control mechanisms associated with farm tractors. It endeavors to improve the functional design of such control valves.

Such a control valve generally has a minimum of two control surfaces, one being in charge of directly controlling the pressure oil flow that effects the pressure build-up in the main line through a pre-actuated (pilotcontrolled) valve. Another control surface serves the purpose of controlling the oil return from the working cylinder.

In the neutral position of a control valve in such a system it is desirable that the oil circuit and pump be pressure compensated. It is possible however that durmg the controlling operations the control valve is moved in its one direction so that even though a throttling of the oil return and a pressure build-up is achieved, this is not sufficient to overcome the back pressure in the working cylinder sufiiciently. In such event the pump would tend to continue counteracting an excess pressure and thereby entail a power loss and a rise in oil temperature.

It is a feature of the present invention to overcome this deficiency and it is a primary object, therefore, to provide a control valve that is movable to a limited degree wherein this movement is accomplished by movement of a portion of the valve independently of other mechanical actuation of the valve and wherein a slight pressure increase in the pressure line causes a control surface of the valve to overlap a control edge portion of the valve bore thereby preventing a throttling thereof when the system is conditioned for actuation of a working cylinder.

Another object of the invention is to provide in a hydraulic system a control valve having two control surfaces one of which selectively controls either the fluid pressure flow through the system or a control circuit that effects a pressure buildup in a circuit through a pilot controlled valve, while the second surface serves to control the flow of return fluid from a work-producing cylinder.

A further object is to provide in a hydraulic system a hydraulic control valve having means associated with a valve spool, wherein said means is movable relatively into engagement with spaced-apart stops to limit the relative movement therebetween.

A still further object is to provide a control valve actuable against spring biasing means by implement attaching control linkage, and having said valve fashioned with means at one end thereof axially movable relative thereto with said movement limited by axially spacedapart stops and wherein said movement is a frunction of the pressure in the pressure line to said valve.

Other objects and advantages will be understood and will become more apparent from the following description when read in conjunction with the accompanying drawings wherein:

FIGURE 1 shows a schematic illustration of a hydraulic control system for farm tractors with draft and position control, the control valve being designed according to a first form of construction of the invention;

FIGURE 2 shows a sectional view of the main control valve, the control surface for controlling the pressure flow being designed according to a second form of construction of the invention.

As can be seen from FIGURE 1, the form of construction provides for two control systems acting on the same control valve. In case of draft control, the control signal or impulse is received from an upper link 1 constituting part of an implement hitch linkage mechanism (not shown) and which is connected to an intermediate lever 2 and pivoted at 3 on a rear Wall 4 of a tractors gear box. A balancing spring 5 permits a certain movement of the intermediate lever 2. The transfer of the control or signal impulse to the control valve is effected by Way of a rod 6, one end of which is in abutting engagement with the free end of the intermediate lever 2 and the opposite end abuts one end of telescopic spring '7 while the opposite end of said spring engages one end of rod 6a, and the opposite end of the latter rod is pivoted to a two-armed lever 9 at 8, the lower end 10 of which rests against an end 11 of the main control valve spool 12 and whose other end is pivotally fulcrumed at 13 to a hand lever 14. For working depth control the fulcrum 13 is adjustable by a hand lever 14 that is pivoted on a shaft 15. The position of the fulcrum 13 determines the working depth of an attached implement, i.e. the force in the upper link 1, at which the main control valve moves into neutral position and thus keeps an attached implement at a certain height by means of the vehicles power lift.

In case of position control, the control signal or impulse is received from a rockshaft 16 in turn operatively connected to the hitch linkage by suitable mechanism (not shown). A rod 17 is eccentrically pivoted to the rockshaft 16 at 18. A slotted hole connection 19 is preferably provided for at one end of the rod 17 in order to render position control ineffective when draft control is employed, while the opposite end of said rod abuts one end of a telescopic spring 70. The opposite end of spring 7a engages one end of rod 17a while the opposite end of the latter rod is pivotally fulcrumed at 60 to a two-armed lever 20, the lower end 21 of which directly acts against end 11 of the main control valve spool 12. The upper fulcrum 613 can be adjusted by the hand lever 22 for pre-selecting the lifting height of the mounted implement.

The hydraulic portion of the system includes a continuously driven pump 23 with constant delivery that draws in oil from the reservoir 25 through line 24 and delivers same through the line 26 to a pre-actuated or pressure biased piston 29 whose front control edge 30 blocks the oil return from line 26 through the annular recess 52 and the line to the reservoir 25 when seated against the tapered bore 31. A restrictor or orifice 34 is located in the head of piston 29 connecting the spaces in front of and behind piston 29. A weak spring 3411 acts on piston 29 in closing direction.

Through a control line 36 the space 35 behind the restrictor 34- is connected With a relief valve 37 that is set to the maximum pressure in the system. The control line 36 further leads to the main valve spool 12. The main spool is longitudinally slidably received in a bore 38 of the valve housing and is pressed against the respective levers 119 and 21 by a spring 39. It is hydraulically pressure compensated and its control surfaces are in charge of controlling the pilot flow for operating the pro-actuated or pressure biased valve 27 and the oil return from the work-producing cylinder 40 by means of which the rockshaft 16, for lifting an attached implement, is actuated. The control line 36 opens into the annular recess 41 that can cooperate with the control edge 42 to block off the pilot fiow from the return through the line 43 to the reservoir 25.

The pressure line 44 to the work-producing cylinder is connected with the annular recess 45 that is released by the control-grooved control edge 46 in lower ing position in order to permit the oil return from the Work-producing cylinder 40 to flow through the line 44, the annular recess 45 and the line 47 to the reservoir 25.

If the system is to be set to lifting the control valve spool 12 is moved to the right as seen in FIGURE 1 so that the control edge 42 closes off annular recess 41. Through the restrictor or orifice 34 the same pressure will build up now in front of and behind the valve piston 29 so that the spring 34a. can close the piston valve 29 and the full delivery flow of the pump 23 is conducted through line 26, check valve 48, and pressure line 44 to the work-producing cylinder 40. When the control valve spool 12 returns to neutral position, as seen in FIGURE 1,

the return from the control line 36 by way of the annular recess 41, the line 43, and the reservoir 25 is released again. The space 35 behind the piston 29 becomes pressureless and at a low circulating pressure determined by the tension of spring 34a the delivery flow of the pump 23 displaces the piston 29 whereby full delivery flow of the pump can return through the annular recess 32 and the line 33 to the oil reservoir. V/ith position control, in particular, it may happen that the attached implement slowly lowers due to leak oil losses. The implement is normally lifted again to the set height by means of a temporary oil delivery. However, it may also happen that the control valve spool 12 moves only far enough so that the control surface 42 just throttles, but does not completely block the passage from the control line 36 to the line 43. In this case the piston valve 29 would not close completely and a pressure would build up that is just sufficient to keep the implement at the present height, i.e. the pump 23 would permanently counteract a certain pressure that corresponds to the load on the lifting device. In order to avoid this the levers 10 and 21 do not act directly on the main spool12 but on a piston 49 which slidingly fits in a bore 50 of the main control valve spool 12. The piston 49 has a transverse bore 51 the diameter of which is slightly larger than the diameter of a pin 52 passing through said bore and fastened in the main control spool 12. Hence, the piston 49 has a small axial movability that is limited to the difference in diameters of said pin and bore. The space 53 in front of the piston 49 is permanently connected with the annular recess 41 through the bores 54.

As long as the main control valve spool is in neutral or lowering position, the annular recess 41 and the space 53 are connected with the reservoir 25 through the line 43 and therefore pressureless. In the position shown in FIGURE 1 the bore 51 is rested against the left side of pin 52 due to the effect of the return spring 39. However, as soon as the control edge 42 approaches the limitation of the annular recess 41 a throttling of the pilot flow occurs and a pressure builds up in the control line 36, the annular recess 41, and the space 53 that is sufficient to move the control valve spool 12 to the right against the force of spring 39 so that the right side of the bore 51 rests against the pin 52. This slight displacement sutfices to ensure that the control edge 42 completely covers the annular recess 41 and switches the system to lifting. A throttle position with the pump permanently counteracting a certain back pressure is thus no longer possible.

FIGURE 2 shows a second form of construction of the invention differing from the first one in that axial movability of the control surface 42 is accomplished by other constructional means. Similar elements will be identified by the same reference numbers as in the first form of construction. In the modified structure a ringed piston 55 is movably mounted on the control valve spool 12. Its axial movability is limited by the stops S6 and 57. The stop 56 is formed by a recess of the control valve spool whereas stop 57 is formed by a ring piece that is slipped onto the valve end and secured by a locking ring 57a. A spring 53 presses the ringed piston 55 against stop 57. When the control edge 42 approaches the end of the annular recess 41 a throttling of the pilot flow occurs and a pressure builds up in the annular recess 41 that causes surface 59 of the ringed piston 55 to move the latter against the force of spring 58 until it rests against stop 56. This displacement is adequate to guarantee that the control edge 42 always completely covers the annular recess 41 as soon as a certain pressure increase in the annular recess 41 is exceeded.

What is claimed is:

1. In a control system for use with a source of fluid under pressure, a fluid reservoir, and a fluid-operated device, the combination comprising: a housing defining a bore, a valve spool mechanically movable in said bore from a neutral position toward a first actuating position adapted to communicate the source with the device and toward a second actuating position adapted to communicate the device with the reservoir, and means for mechanically moving said valve spool in said bore, said valve spool including fluid pressure responsive means for moving said valve spool toward said first actuating position upon mechanical movement thereof toward said first actuating position.

2. In a control system, the combination comprising: a housing defining a bore and first and second fluid passages communicating with said bore, said first and second fluid passages adapted to communicate respectively with sources of relatively high and low fiuid pressure, a valve spool movable in said bore between first and second positions respectively communicating said fluid passages and blocking communication between said fluid passages, and mechanical means including lost motion means cooperable with said valve spool for effecting movement thereof between said positions, said valve spool having surface means exposed to said first passage, said valve spool being movable toward said second position independently of said mechanical means in response to the build-up of fluid pressure acting on said surface means as movement of said valve spool toward said second position is effected by said mechanical means, said independent movement of said valve spool being limited by said lost motion means.

3. The invention according to claim 2, said lost motion means including a piston engageable by said mechanical means and movable within said valve spool be tween fixed limits established thereby.

4. The invention according to claim 2, said lost motion means including a sleeve engageable by said mechanical means and movable about said valve spool between limits established thereby.

References Cited by the Examiner UNITED STATES PATENTS 450,767 4/91 Gold l37517 X 547,506 10/95 Sleigh 1375l7 X 2,010,645 8/35 Roberts 25l-l4 2,964,908 12/60 Pomper 137-62l X 3,088,283 5/63 Furia et a1. 13762l X 3,102,550 9/63 Shand 25l77 X M. CARY NELSON, Primary Examiner. 

1. IN A CONTROL SYSTEM FOR USE WITH A SOURCE OF FLUID UNDER PRESSURE, A FLUID RESERVOIR, AND A FLUID-OPERATED DEVICE, THE COMBINATION COMPRISING: A HOUSING DEFINING A BORE, A VALVE SPOOL MECHANICALLY MOVABLE IN SAID BORE FROM A NEUTRAL POSITION TOWARD A FIRST ACTUATING POSITION ADAPTED TO COMMUNICATE THE SOURCE WITH THE DEVICE AND TOWARD A SECOND ACTUATING POSITION ADAPTED TO COMMUNICATE THE DEVICE WITH THE RESERVOIR, AND MEANS FOR MECHANICALLY MOVING SAID VALVE SPOOL IN SAID BORE, SAID VALVE SPOOL INCLUDING FLUID PRESSURE RESPONSIVE MEANS FOR MOVING SAID VALVE SPOOL TOWARD SAID FIRST ACTUATING POSITION UPON MECHNICAL MOVEMENT THEREOF TOWARD SAID FIRST ACTUATING POSITION. 